Pls help

The acceptable times are;

a) Between 10:00 PM and 11:00 PM

b) Between 7:30 AM and 9:00 AM

Step-by-step explanation:

From the question, we have that Mark an Hans are not able to c h a t in the times between;

a) 9:00 AM and 4:30 PM

b) 11:00 PM and 7:00 AM

Local times

Therefore they can c h a t at times between;

a) 7:00 AM and 9:00 AM

b) 4:30 PM and 11:00 PM

When the time is 1:00 AM in Berlin, it is 10:00 AM in Sydney

Therefore, the time  difference between Sydney, Australia and Berlin, Germany = 10:00 AM - 1:00 AM = 9 hours

Therefore, when Mark can c h a t, the time in Berlin will be;

a) 7:00 AM -09:00 = 10:00 PM and 9:00 AM - 09:00 = 0:00 AM

Which gives;

10:00 PM and 0:00 AM

b) 4:30 PM - 09:00 = 7:30 AM and 11:00 PM - 09:00 = 2:00 PM

7:30 AM and 2:00 PM

Therefore, the acceptable times they can c h a t is found by overlapping the above times at Hans location in Berlin with the times Mark can c-hat in Sydney, Australia to get;

The acceptable times are between;

a) 10:00 PM and 11:00 PM

b) 7:30 AM and 9:00 AM